1. Unit2: Life Over Time Chapter 6: Evolution of Living Things 6.1 Earth has been home to living things for about 3.8 billion years 6.2 Species change over time 6.3 Environmental changes can affect populations 6.4 Many types of evidence support evolution

2. Natural Selection explains how living things evolve Overproduction:  A plant or animal that reproduces usually makes more offspring than can possibly survive (than the environment can support): Ex: several thousand salmon eggs, not all hatch, a few hundred survive disease or predation, several dozen reach adulthood, and few will successfully reproduce Variation  Species have natural differences/variations in traits – ex: fin size These are passed on from one generation to the next Genetic material may change – new variation (mutation) Reproduction: passes these traits to offspring Adaptation  A mutation can make an individual better able to survive An advantage in the particular environment; ex: tail shape – swim faster Selection  Particular adaptations lead to survival long enough to reproduce  That adaptation becomes more common in the next generation of offspring Population: group of individuals of the same species that live in a particular environment or area Genetic variation: differences in DNA in a population Environmental factors: conditions that affect survival – include food supply, habitat, predators, and disease

4. 6.3 Environmental changes can affect populations Before, you learned:  Species change over time  Organisms need resources such as energy and space  Organisms in an ecosystem affect one another Now, you will learn:  How populations increase and decrease in size  What factors affect population size and survival  How a species can become extinct

5. Population size is limited by environmental conditions What if a population reproduced without limits?  Pair of fruit flies  200 eggs in two weeks…  > eight months, the mass of fruit flies would be more than the mass of Earth In nature, Darwin notice:  All populations have the ability to grow rapidly over time  Populations tend to remain about the same size Populations could increase greatly but usually didn’t…why?

6. Population size is limited by environmental conditions Resources – food, water, shelter, mates, etc – are limited  Natural limits to population growth Populations must be stable in order to survive  Cannot have too many or too few members for very long

7. Populations increase through births and immigration More than enough resources  population size increases  Key factor is high birth rates # births > # deaths  Immigration: movement of individuals into a population Wind blows seeds, deer travel to new forest Can also help a population that is decreasing in size to become stable

8. Many factors limit population size Decline can happen two ways:  # death > # births  Emigration: movement of individuals out of a population Possibly to an area with more resources or fewer individuals Can help stabilize a population growing too quickly Limiting factors: environmental factors that limit population size  Include food, water, light, space, shelter, and air  Also includes other organisms, and sudden changes in the environment (storm, fire, etc.)

9. Competition Can be a matter of life and death Can be between the same species or different species Ex: wolves competing for food  Too many wolves, not enough resources: some may emigrate Unhealthy, very young, or very old, may starve to death or fall prey to predators

10. Predators Prey on other animals Major role in limiting population size  keep the population of their prey stable Can keep the prey from outgrowing resource supplies Can keep rodents and other pests in check!

11. Disease As a population grows, close contact increases chance of disease spreading  Those lacking natural defenses may die or grow sick  Ex: 1900s – American chestnut trees infected by fungus By 1950, almost all had died

12. Catastrophic Events Wildfires, hurricanes, floods, droughts, etc Can wipe out an entire population Ex: drought affecting certain plants – impacts animals that feed on those plants  Could also affect animals that use it as shelter

13. The survival of a species depends on its ability to adapt to change Extinction can occur when a species can no longer survive in their environmental conditions  Limiting factors - resources, predators, etc. Usually, one population at a time  Individuals better adapted to change are more likely to survive and produce offspring Genetic variation assists in there being a chance that some survive environmental changes

14. How Extinction Happens Happens when ALL populations of a SPECIES die out Maybe caused by a change in the environment  Ex: disease, loss of habitat Loss of population members decreases genetic variation Chances members of finding a mate A disease can change a species’ environmental condition  Some individuals may have a natural resistance (due to genetic variation) – they survive Repopulation depends on how long it takes a species to reproduce Ebola virus

15. Extinction and Species Replacement Extinction is part of the cycle of life on earth Makes room for other species to thrive Mass extinctions are usually followed by the sudden appearance of new species  Ex: The Cretaceous (K-T) extinction 65 million years ago wiped out the dinosaurs… Some small mammals that had existed survived and were then able to thrive (K-T extinction is thought to be caused by an asteroid impact triggering earthquakes and volcanic eruptions, leaving a lot of dust in the air – decreased sunlight:  decreased photosynthesis – affecting food supply  Lowered temperatures  Mammal’s fur helped them adapt to a cooler climate

17. Select marine species